I use Nikon D5000 with 18-55mm f/3.5-5.6G VR lens. Pictures come out with high dark contrast colors?

I'm not a professional photographer, and I don't aim to be. I just love taking pictures for a hobby. I have had this camera for about a year. Night pictures with flash come out to be good, but for day time, the colors are so faded. As in blue sky will look more like a grayish sky. I have tried so many settings and compared pictures, but still haven't found a good setting for day time outdoor shooting. I'm planning to buy 55-200mm lens, would it help to get any brightness into my photos. I want them to be more realistic with the original colors. For example, when I take picture of something red, it is more likely to be brownish.